The blades of a propeller device are typically symmetrically arranged on a shaft around a central rotational axis to allow the blades to rotate around that axis. Depending on the purpose and design of the propeller device, the blades are rotated either by the flow of a fluid (e.g. gas or liquid) passing therethrough and/or by a motor or by a manually powered mechanism. Here the term “turbine blades” will be used for designating working blades of the propeller device, i.e. those blades, which upon exposure to the flow of fluid transmit forces to and from the fluid medium. So for example when the fluid is air and when the propeller device is an aircraft rotation of the turbine blades create thrust enabling propelling the aircraft.
In aerodynamics an angular position or inclination between a chord of a turbine blade and direction of flow of fluid is known as angle of attack. The value of this angle is important for proper and efficient functioning of a propeller device.
Blades inclination adjusting mechanisms are commonly used in propeller device for setting a predefined angle of attack. By virtue of this provision efficiency of the propeller device can be significantly improved, e.g. by reducing drag as it is known in aircrafts or watercrafts.
There are known in the art various attempts to provide automatic control of angular position of the blades for setting the desired inclination angle. Most known control systems for adjusting the inclination angle of blades, which include dedicated sensors configured for sensing direction and intensity of incoming fluid flow and reporting this data to a central unit which controls the turbine blades and adjust their angular position accordingly.
In propelling devices such as aircrafts or watercrafts in which one or more turbine assemblies are used for propelling a vehicle, hydraulic control mechanisms are used for gaining or reducing thrust by changing the attack angle of the propeller blades.
In many systems such as aircrafts and wind turbines adjustment of angular position of the blades is effected by forcible pivoting the blades, wherein each blade is rotatable over its corresponding pivot axle.
Below are listed same examples of propeller devices provided with forcible control of blades angular position.
In WO2007012487 is described wind power plant comprising a rotor that is equipped with adjustable rotor blades and a central control device allows adjusting the rotor blades using pitch devices.
In CN101629553 is disclosed wind power plant comprising plurality of rotor blades, a blade inclination drive, a rotor shaft, an electric generator, and a control unit for controlling the operation of the power plant, in particular for adjusting the blade inclination under the control of the control unit.
There are known also propeller devices, devised for automatic self-adjusting the blade inclination angles depending on centripetal forces applied to auxiliary masses.
In US2012/0014794 is disclosed a self-setting and self-powered system for adjusting the blades inclination of a wind turbine such that they have a high angle of attack when parked to promote early start up, move to their ideal setting angle for normal running and feathers the blades to limit the rpm and reduce load in storm condition.
In AU-331695/84 is described a load sensing propeller for use in marine craft. The inclination of the blades can be automatically adjusted such that the propeller performs effectively in a variety of operative conditions, e.g. in getting a craft underway and in maintaining cruise speed.
In U.S. Pat. No. 4,693,671 is described reversible self-adjusting propeller device, in which there are provided control blades and thrust blades connected together and pivotally mounted on a hub. In response to variation of load acting on the device the control blades automatically pivot in relation to the hub axis at generally constant angle and this causes corresponding pivoting of the thrust blades. In this propeller device the thrust blades are mounted on the hub in such a manner that they can pivot on their axles and accordingly their angular position can vary when they are exposed to flow of fluid. Furthermore, the control blades are pivotally mounted on their axles while their axles can displace within elliptical wedge-shaped recesses made in the hub. As a result the thrust blades pivot at a changing inclination angle in relation to the hub axis while the control blades do so at a generally constant angle. As a consequence of this design the angular position of the thrust blades is controlled not solely by angular position of control blades and it is not possible to unequivocally set and maintain the desired angle of attack of the thrust blades.
In general one can see that despite numerous attempts to devise inclination control for propeller device, this long felt problem still requires proper solution.